Resilient head lock bolt



Feb. 27, 1951 c. E. PLACE 2,543,705

RESILIENT HEADLOCK BOLT Filed May 15, 1948 INVEN TOR.

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Patented Feb. 27, 1951 r 2,543,705 RESILIKENT HEAD LOCK BOLT Charles E.'s. Place, Highland Park, Mich.

Application May 15, 1948, Serial No. 27,345 In Great Britain November19, 1947 .4 Claims. (01. 151-32) This invention relates'to animprovement in bolts or cap screws (referred to herein as bolts and hasfor an object the provision of a bolt which can be made economically inavailable automatic machines, and which has, as compared to ordinarybolts, a greater resistance to accidental loosening (resulting, forinstance, from vibration) and to breakage.

Another object is the provision of such a bolt in which a criterionexists for accurate determination of the axial loading of the boltindependently of the torque with which it is applied.

A further object is the provision of such a bolt which can be made witha low ratio of rejects without requiring special grades of steel.

Such bolts are characterized, briefly, by the provision of an annularrecess in the under face of the bolt head at its line of juncture withthe shank, in combination with the formation of one or morediametrically disposed slots or grooves in the upper face of the head. 7

Practical embodiments of the invention are shown in the accompanyingdrawings, in which:

Fig. 1 represents a top plan view of one form of the bolt;

Fig. 2 represents a side elevation of the bolt shown in Fig. 1;

Fig. 3 represents a vertical axial section taken on the line III-III ofFig. 1;

Fig. 4 represents a side elevation of a modified form of bolt, the topplan view of which is the same as Fig. 1;

Fig. 5 represents a vertical axial section of the bolt shown in Fig. 4;

Fig. 6 represents a top plan view of another modified form of the bolt;

Fig. 7 represents a vertical axial section taken on the line VII-VII ofFig. 6;

Fig. 8 represents a top plan view of another modified form of the bolt,and

Fig. 9 represents a vertical axial section taken on the line IX-IX ofFig. 8.

Referring to the drawings, and particularly to Figs. 1, 2 and 3 thereof,the bolt is shown as having a shank I and hexagonal head 2, conformingits outside dimensions to standard or accepted bolt design. An annularrecess 3 is formed in the under face of the head at the line of juncturewith the shank, leaving a generally annular .under bearing surface; lspaced from the shank. The upper part of the head is provided withdiametrically disposed vertical slots 2 approximately between one-thirdand one-half the depth of the head. The bottoms of the grooves 5 arecurved in profile (Figs. 2 and 3') so that the grooves are deeper at themiddle and shallower at each end, this form resulting conveniently fromthe cutting of the grooves by means of a circular saw toward which thebolt is fed in the direction of the bolt axis. The grooves arerelatively narrow, their width being such thatthe amount of materialremoved to form them is generally less than the amount of materialremaining in the upper part ofthe head after they are formed.

7 According to Figs. 4 and 5, the bolt head 6 is provided with slots orgrooves l, disposed inthe same manner as the grooves 5 of Figs. 1 to 3,but having fiat bottoms parallel to the upper and lower faces of thehead. The grooves i may conveniently be formed by feeding the boltblanks sideways along a path tangential to a circular cutter or saw.Desirable limits of depth and Width of the grooves are as describedabove.

grooves (as shown) or may be extended slightly farther into the head ifdesired.

While the provision of slots or grooves disposed as described above isconsidered to be preferable, certain of the advantages of the inventioncan be obtained (in a more economical manner) by the form ofconstruction shown in Figs. 8 and 9. In this case the head 9 is providedwith a single diametrically disposed groove Ill, extending to a depth ofapproximately half the head depth, the sides of the groove being more orless tapering or flaring for convenience in manufacture as by a hot orcold shaping operation.

In all cases it will be understood that the under face of the head isformed to provide a bearing surface spaced from the shank, the provisionof the annular recess (3,.Figs. 1 to 3) being an acceptable way ofachieving this result.

Because the under bearing surface is spaced from the shank and the upperpart of the head is relieved, particularly at its center, by theformation of a groove or grooves, the material remaining between thelower annular recess and the bottom of the upper groove or grooves actsas an elastically flexible diaphragm, reinforced by the segments formedbetween the slots, permitting a substantial increase in elasticelongation of the bolt and preventing it from being loosenedaccidentally, as by vibration. At the same time the materialconstituting the diaphragm retains a resistance against shearingstresses greater than that in the threads, so that the effectivestrength of the bolt is not reduced. Compared to ordinary bolts of thesame size and material, the bolts described herein, when applied withthe same tightening torque, show less (axial) tensile strain andconsiderably greater release torque. Thus, if applied up to the sametensile strain, the release torque (and security against loosening) canbe increased still more (greater than 50% in some cases).

In making the bolts of Figs. 1 to 7 there are no unusual shapingstresses and the same grades of steel can be used as inordinary boltswithout increasing the number of rejects. The bolt of Figs. 8 and 9 mayrequire slightly better steel, which is fully compensated for by thereduction in manufacturing stepsthe single groove being formed in thesame operation or series of operations with the formation of the headitself.

An important advantage of the bolts slotted or grooved as shown residesin the fact that the tightness with which they are applied can bedetermined in terms of the axial loading of the bolt, instead of theunreliable factor of torque; variations of friction in the threads andseat result in wide variation of loading even when the applying torqueis uniform. In the bolts disclosed herein the flexing of the diaphragm,within the elastic limit of the head, causes the sides of the slots orgrooves to close toward each other,- the amount of such closing being adirect function of the axial loading of the bolt which can be calibratedand accurately guaged.

It appears that substantially the same-results can be obtained byforming the slots or grooves through the hexagon corners of the head asby having them terminate in the middle of the flats.

The construction shown as applied to hexagonal heads is also adaptable,with the same-advantages, to heads of other shapes such as square orround.

What I claim is:

1. A bolt of the character described comprising, a hexagonal head and athreaded shank, the under face of the head being provided with anannular recess adjacent the line of juncture of said face with the shankand having a substantially flat annular bearing surface lyingperpendicular to the axis of the bolt and spaced from the shank, theupper face of the head being pro vided with three intersectingdiametrically disposed slots extending vertically into the head adistance not less than approximately one-third of the head depth and notgreater than approximately one-half of the head depth and completelyacross the head through the middle of opposite flats, and the bottoms ofsaid slots forming a substantially continuous surface lying, at least atthe axis of the bolt, perpendicular to said axis, whereby the slots andrecess will permit elastic distortion of the head when the bolt istightened.

2. A bolt according to claim 1 in which the bottoms of the slots lie ina plane parallel to the under face of the head.

3. A bolt according to claim 1 in which the bottoms of the slots lie inan arc, the center of which is on the axis of the shank and above theupper face of the head.

4. A bolt according to claim 1 in which an enlarged recess is formed atthe crossing point of the slots, the bottom of said recess lying atsubstantially the level of the bottoms of the slots.

CHARLES E. S. PLACE.

REFERENCES CITED The following references are of record in the fileof't-hispatentr UNITED STATES PATENTS

